1. Technical Field of the Invention
This invention relates to data transmission systems, e.g., Integrated Services Digital Network (ISDN) and methods of operation. More particularly, the invention relates to a data transmission system and method for interconnecting sending and receiving analog devices, primarily through data channels and without device identification.
2. Background Discussion
It is now classical to exchange digital data between two digital Data Terminal Equipments (DTE) over the Integrated Service Digital Network (ISDN).
The DTE are connected to the ISDN network by means of Terminal Adapters the function of which is to set the communication through the ISDN D channel and then, to monitor the quality of the line and to wait for the disconnection.
It is also possible to transport data from an analog Terminal to another analog Terminal (such as two fax devices) over the ISDN network after the analog signals have been encoded into digital form by a pulse code modulation (PCM) or other type of coding.
A problem is raised when several analog Terminals are multiplexed and share the same line. There is generally no problem in the switched network (PSTN) environment insofar as the difference in the setting delay of each equipment is used to avoid that two or more devices answer simultaneously. But, in the ISDN network environment, it is necessary to transport some information elements used to identify the analog device being called. Such information elements are specific words within the D channel. Unfortunately, the protocol used for the D channel (LAPD) being restraining, these information elements may not be recognized in some cases or not transported at all by the carrier as it is the case in some countries.
Accordingly, an object of the invention is to provide a reliable method of setting the communication over the ISDN between a transmitting analog device and a receiving analog device among a plurality of receiving analog devices.
Another object is a system and method for interconnecting sending and receiving analog devices in a data transmission system primarily through data channels in such systems.
Another object is a system and method for interconnecting sending and receiving analog devices without identification using tones and data channels of the data transmission system.
Another object is a system and method for interconnecting sending and receiving analog devices in a data transmission system using a data base for connecting unrecognized tones to the most appropriate analog device.
Another object is a system and method for interconnecting sending and receiving analog devices in a data transmission system in which a data base is updated for connecting unrecognized tones to the most appropriate analog device after establishment of a successful connection.
These and other objects, features and advantages are achieved in a system and a method of setting data communication between a transmitting analog device and a receiving analog device in a data communication system wherein a first plurality of transmitting analog devices connected to a transmitting Terminal Adapter interfacing a communication network including an Integrated Service Digital Network (ISDN) can transmit data to a second plurality of receiving analog devices connected to a receiving Terminal Adapter interfacing the same network. The system is characterized in that the calling tone sent by the transmitting analog device for identifying and initializing the receiving analog device is transported over the ISDN network within the B channel.
The method comprises the following steps:
(a) After the transmitting analog device has dialed the identification number of the receiving Terminal Adapter, the transmitting Terminal Adapter sends a SETUP message containing the identification number to the receiving Terminal Adapter, this message being transported over the ISDN network within the D channel;
(b) The receiving Terminal Adapter connects the receiving analog device to the ISDN network by allocating a B channel to the receiving analog device;
(c) The receiving Terminal Adapter sends back a CONNECT message to the transmitting Terminal Adapter to indicate that the communication setting is accepted;
(d) The transmitting Terminal Adapter connects the transmitting analog device to the ISDN network by allocating a B channel to the transmitting analog device;
(e) The calling tone generated by the transmitting analog device is transported from the transmitting Terminal Adapter to the receiving Terminal Adapter over the ISDN network within the B channel; and
(f) A ring signal is sent by the receiving Terminal Adapter to the receiving analog device.